Human mast cells originate from pluripotential progenitor cells and migrate as immature cells from the bone marrow to tissue sites including the skin, lung and gastrointestinal tract. There these precursors mature and participate in both innate and acquired immune responses with production of cytokines and other inflammatory mediators. Mast cell growth and development thus may occur in a tissue that interfaces with the external environment, potentially exposing mast cells during their development to bacterial products which could have an impact on their subsequent behavior. Consistent with this idea is the observation that mast cells are known to express Toll-like receptors (TLR) 1-7. We thus explored whether bacteria-derived products alter the growth and development of CD34+-derived human mast cells by performing long and short-term cultures to which we added LPS or PGN. We followed specific mast cell characteristics including growth;surface FcepsilonRI and CD117 expression;degranulation, LTC4 and PGD2 release;protease expression, and cytokine release. Over 6 wks of culture, LPS had minimal effect on CD34+-derived human mast cell numbers but increased CD117, tryptase and chymase expression. PGN inhibited CD34+-derived human mast cell development. For mature mast cells, LPS in the presence of rhSCF (10 ng/ml) increased CD117, tryptase, chymase and carboxypeptidase expression, primarily in CD117low CD34+-derived human mast cells. LPS decreased FcepsilonRI expression and granule release;but had no effect on LTC4 and PGD2 production. PGN reduced CD34+-derived human mast cell numbers;and CD117 and tryptase expression. IL-1 and IL-6 (in addition to IL-8 and IL-12) were detected in short-term culture supernatants of LPS treated cells, and reproduced the increases in CD117, tryptase, chymase, and carboxypeptidase expression observed in the presence of LPS. Comparative studies with mouse bone marrow-derived mast cells from wild type, but not TLR4 knockout mice, showed increases in mRNA of mouse mast cell chymases MMCP-1, MMCP-2 and MMCP-4. We thus concluded PGN inhibits human mast cell growth, while LPS exerts its primary effects on mature mast cells by altering cytokine production and protease composition, particularly at low concentrations of SCF. These data thus demonstrate the ability of bacterial products to alter human mast cell mediator production, granular content, and number which may be particularly relevant at mucosal sites where mast cells are exposed to these products. In studies relating to the biologic expression of mast cells, we were aware that human mast cells are associated with modulation of vascular permeability, angiogenic processes, wound healing and asthma where the protein angiogenin (ANG) has been implicated. We thus hypothesized that human mast cells express and secrete ANG. ANG expression was evaluated in the LAD2 human mast cell line, the human mast cell line 1 (HMC-1) and CD34+-derived human mast cells following exposure to live E. coli, TLR ligands or neuropeptides;and following FcepisalonRI aggregation. Microarray analysis revealed that ANG is upregulated by LAD2 cells exposed to live E. coli. qRT-PCR analysis revealed that LAD2, HMC-1 and CD34+-derived human mast cells constitutively expressed ANG mRNA and that it was up-regulated by exposure to E. coli. Activation of CD34+-derived human mast cells by FcepsalonRI aggregation resulted in the release of small amounts of ANG , whereas compound 48/80, nerve growth factor, lipopolysaccharide, peptidoglycan and flagellin activated CD34+-derived human mast cells to secrete >160 pg/mL ANG. These observations are consistent with the conclusion that human mast cells both store and secrete ANG to a variety of stimuli;and suggest that mast cell-derived ANG is available in the subsequent inflammatory response. In a project relating to allergic inflammation, we noted that loss of SOCS7 in mice is associated with severe skin disease. We sought to explore the underlying mechanisms. Data obtained revealed that Socs7-/- mice have increased serum IgE and IgG1 production and exhibit an increased mast cell infiltrate, as well as un-provoked mast cell degranulation in the dermis as compared to controls. In vitro, bone marrow derived mast cells from Socs7-/- mice are hyperactive to IgE-mediated stimuli, with elevated production of proinflammatory cytokines (IL-13, IL-6, TNF-). Further, activated Socs7-/- bone-marrow derived mast cells have increased IL-7R transcript, which is part of the heterodimeric receptor for TSLP. Finally, lack of SOCS7 was accompanied by an increase in TSLP mRNA and protein production by mast cells following FcepsilonRI aggregation. These data implicate SOCS7 in the modulation of allergic inflammation and demonstrate that SOCS7 is involved in the regulation of TSLP signaling in mast cells.